| Some time ago, I trained users on Network Analysis and accumulated 1.0 scattered data. I hope it will be helpful to you. Network Type
(1) Transportation Network: it is an undirected network. Indicates that the edge of the network has a direction. You can freely define the direction, speed, and end point of the network. For example, a truck driver can decide on which road to start, where to stop, and where to adopt. You can also set limits for the network, for example, single line or no line. In ArcGIS, the transportation network is created through network dataset.
(2) utility network: Directed Network type, which means that the substances flowing in the network must follow the rules defined in the network. The running paths are pre-defined and can be modified, but it cannot be modified by the material itself, but by the network engineers to modify the network rules so that the network flow direction can be changed by setting the node opening status. In ArcGIS, utility network is simulated by geometric network.
Introduction to transportation network
The ArcGIS network analyst analysis module uses a network that is stored in the network dataset. Network dataset is created by feature elements and can be used to express complex scenarios, including multimodal traffic networks. It can also contain multiple network attributes to simulate network constraints and hierarchies.
Network dataset contains the following three types:
(1) network dtaset: the data source for creating a network is stored in personal or enterprise Geodatabase. Because many data sources can be stored, you can build a multimodal network.
(2) shapefile-based network Dataset: created based on the polyline shapefile. You can also add shapefile turn feature class. This network dataset does not support multiple edge types, it cannot be used to create multimodal networks.
(3) ArcGIS network analyst can also read SDC network dataset for network analysis, rather than creating network Dataset Network elementsThree types are available: edges, junctions, and turns. connectivity group
to define the connectivity of ArcGIS network analyst, you must first define the connectivity group. Each edge source can only be assigned to one Connectivity Group, while junction source can be assigned to multiple connectivity groups. You can connect the edge of different connectivity groups only by setting Junction to two or more connectivity groups. Connectivity Group is used to create a multimodal transportation network.
the following three connectivity models supported by network Dataset:
(1) connecting Edges Within a connectivity group
you can set "endpoint connectivity ", you can also set "any vertex connectivity ". In the first method, the edge and the edge can only be at the end, and the second method can be at any position of the edge
(2) connecting edges through junctions across connectivity group
connects edges in different connectivity groups through the junctions connections shared by different connectivity groups.
(3) Elevation fields
is used to check the connectivity of line endpoints in network dataset. Each edge feature has two fields to describe the elevation of each endpoint. Network attribute
Network attribute is mainly used to set the flow attributes of the network, including:
Name:
Usage type:
Unit: centimeter, meter, etc.
Data Types: Boolean, integer, float, double
Use by default:
Cost: for example, the time required to walk a certain path
Descriptors: The description of a certain road, such as the road speed limit and the number of traffic lights.
Restrictions: for example, a line is prohibited or one-way
Hierarchy: for example, classification of Roads Types of evaluators used by a network
You need to set values for network attributes. evaluators is usually used to obtain the attribute values from network source. There are four evaluators:
Field Evaluator: Use the value of the attribute field;
Field Expression Evaluator: Uses attribute fields to construct a calculation expression;
Constant evaluators: assign a constant;
VBScript evaluators: Execute VBScriptCodeIs mainly used to assign complex attribute values.
Each junction source and turn source requires an evaluator, and each edge source requires an evaluator in every direction of Two-edges. Turns in the network Dataset
There are multiple types of turn, which can be multi edge turn or U-turn. In ArcGIS, the turn is transformed by the turn feature class. These turn feature classes are all polyline feature classes. The turn feature class must be in the same feature dataset as other network elements and have the same spatial reference. It does not participate in connectivity groups or have elevation information. Turn has at least two edges and up to 20 edges. Setting directions ctions
The Network dataset that supports ctions must meet at least the following requirements:
Has the Length attribute, including the length unit;
At least one edge source;
At least one text field exists on edge source. Creating a network Dataset
Step 1: Prepare feature dataset and source;
If you want to create a Geodatabase-based network dataset, the data source that participates in the network creation must be in the same feature dataset; if you want to create a network based on shapefile, you need to store the participating elements in the same folder.
Step 2: Set Properties for the data source that creates the network dataset and add attribute information for the network;
Ensure that the data source contains the attribute value-distance, travel time, and so on that you can set network resistance information. Finally, the field names of these attribute values are named in the corresponding unit so that the system can automatically identify them. For example, you can set the field name to minutes for travel time. For linear elements, if the resistance values are different in different directions, you should set attribute fields for the two directions, such as "ft_minutes" and "tf_minutes ".
If you are creating a network for a single line, edge source must contain a field to specify the one-way street attribute. You can name the field storing this attribute "one_way" or "oneway ". Create an evaluator to assign a value to this field:
"Ft" or "F" indicates a single line along the digital direction;
"TF" or "T" indicates a single line in the opposite direction of digitalization;
"N" indicates a prohibited line;
If it is another property value, it indicates that both sides of the line are accessible.
If you want to simulate overpasses and underpasses through the Z-elevation or Z-level values, you must include two integer fields in the edge attribute field. The elevation of each node of the edge is represented by one Field. If a field is named "f_elev" "t_elev" or "f_zlev"" t_zev ", the system can automatically recognize it as an elevation field.
If you want to save the direction information in the network, the edge attribute field must contain the direction information, such as the road level, high-speed obstacle, and boundary information.
Step 3: Prepare the turn feature class and add the turn information;
When creating a feature dataset, the turn information is optional. If you save the turn information in the turn table, you must convert it to the turn feature class. In addition, the attribute table of the turn feature class also contains attribute fields to retain the network attribute information such as the turn impedance and turn restriction (a certain bend can only be converted by a truck.
Step 4: Use the new network dataset Wizard to create a network Dataset
Name the network dataset, set the data source, create connectivity, specify the elevation data, specify the turning data source, define attributes, and determine the direction rules.
Step 5: build network Dataset
This process will implement: creating network elements, creating connectivity, and assigning attribute values to Network Properties Analysis functions provided by network analyst
Finding the best route
ArcGIS network analyst can analyze the optimal path between a vertex and a vertex. You can set the position of a vertex in three ways: (1) Add a vertex on the screen. If the vertex you add is not on the path, the system automatically blocks the point to the near point according to the snapping settings. If the distance from the point to the line is greater than the set occlusion value, it cannot be implemented. You need to reset snapping; (2) input address; (3) to import a location from an existing feature class or feature layer. The order between points in the optimal path can be set by the user or automatically set by the system.
Possible Optimal Path analysis includes the shortest path, shortest path, and the path of the most scenarios. The path analysis content can be achieved by setting impedance. Finding the closest facility
Find the nearest facility: you can set a cutoff cost. Once this setting is exceeded, it will not be analyzed. Once the nearest facility is found, the functions that can be achieved include the path to the nearest facility, travel expense, and direction. Finding service areas
Network Service area is the region of all streets that can be reached within the set threshold. For example, the 5-minute service area at a certain point is the region of all the streets that can be reached within 5 minutes from that point.
Accessibility indicates the degree of ease to arrive at another location from a certain point. In ArcGIS, accessibility can be set through travel time, distance and any other impedance. Creating an OD cost Matrix
The origin-destination (OD) Cost matrix can be created between multiple source points and endpoints. Od cost matrix is a table that contains the total impedance from each origin to each destination. When expressed on a map, the path from origin to destination is expressed in a straight line. Introduction to geometric Network
Geometric network is mainly used to simulate real-world resource networks such as water networks, power grids, gas networks, and telephone services.
The geometric network consists of a set of interconnected edges and junctions, and contains the connectivity rules. Must be built in the feature dataset of Geodatabase. The feature class is used as the data source of junctions and edge.
Geometric network includes two main elements: edges and junctions
In the network, edge and junctions are topologically connected to each other: edge and edge are connected at junctions. The elements of a certain edge flow are to flow to other edges through junctions.
There are two types of edges:
Simple edges-connects two junctions S, and each end of edge connects one junction;
Complex edges-generally, at least two junctions s are connected at the endpoint, and many junctions s can be connected in the middle of the edge. For example, multiple MPs queues can be connected on the supervisor channel.
There are two types of junctions:
User Defined junctions ctions: the junctions ctions network generated based on the user-defined point source when building the geometric network;
Orphan junctions: when the first edge feature class is added to the geometric network, a simple junction feature class is created, called orphan junction feature class, which is mainly used to maintain the integrity of the network. When you add other junric feature, orphan junctions ctions at this point will be deleted. In addition, when you delete the geometric network, orphan junctions ctions will also be deleted.
When a geometric network is created, a corresponding logic network is created to represent the connection relationship between the modeled elements and implement tracing and flow computing. Logic Network is composed of a series of tables and maintained by ArcGIS. When the geometric network is updated or deleted, the logic network is automatically updated. Sources and sinks
The flow direction of network elements is calculated from sources and sinks. The flow from sources is collected to sinks. You can set junctions ctions to sources or sinks when creating a geometric network. Once it is set to source or sink, add the ancillaryrole field to the Attribute Table to record its type. Network Weight
A weight can be set to indicate the environment in which network elements flow, so that weight of the network can be set using the feature attribute of the network involved. Enable and disable feature
Edge and junctions in the geometric network can be set to enabled or disabled in the logic network. The enabled or disabled status of the network is set by the feature attribute field enabled. The optional properties are true and false. When you create a geometric network through a simple feature class, this field is automatically added as an input element, and the default attribute value is true. Connectivity
In real life, not all elements of the geometric network can be connected to each other, and the network connectivity created by the system may not be suitable. Users can modify the connectivity as needed, the method is to click the geometric network created in arccatalog and select the connectivity panel in properties to implement connectivity settings.
Connectivity rule can be created in two ways: edge-junction connectivity and edge-Edge Connectivity |
